class Plugin:
    pass


class Plugin1(Plugin):
    def __init__(self):
        print("plugin 1")

    def hello(self):
        print('hello plugin1')


class Plugin2(Plugin):
    def __init__(self):
        print("plugin 2")

    def hello(self):
        print('hello plugin2')


if __name__ == '__main__':
    plugins = []
    for cls in Plugin.__subclasses__():
        obj = cls()
        plugins.append(obj)

    for plugin in plugins:
        plugin.hello()
